The invention relates to a method for the identification of incorrectly orientated parts and/or parts departing from a predetermined master, which by means of a conveying means are moved past at least one camera for registering shapes of the parts, in the case of which given a pre determinable departure from stored master values the respective part is identified as being faulty and/or is removed, and to an apparatus for the performance of the method.
In the case of many items of manufacturing equipment, assembly plant, packaging means or the like it is necessary for the parts to be processed to be pre-orientated and to be supplied with the prescribed orientation. The supply of faulty or damaged part or of parts departing from a master or pattern or of non-faulty but incorrectly orientated parts in such further processing by machine frequently leads to damage of the plant itself, to interruptions of production or to other undesired consequences. For this reason it has long been a practice to provide testing means at the input end of such processing means by means of which the correct orientation and/or correct dimensions of the parts may be checked. So-called rejects, which do not pass such a test, are sorted out and only the satisfactory parts are conveyed on farther.
A conventional test means, disclosed for example in the German patent publication 2,628,358 C1, comprises a camera, with the aid of which the shapes of the parts run past the camera by the conveying means are examined. The respectively registered shapes are compared with stored shapes. If they are found to be the same, it is a question of an acceptable part or otherwise, allowing for tolerated inaccuracies it is a question of a reject, which is to be treated accordingly. The disadvantage of the known method is that in the case of this method all departures from the shape of the master are taken in principle to be equivalent. If the tested parts for example have a screw thread, and more particularly a precision screw thread, same will only affect the shape to an extremely small extent and the tolerated inaccuracy will have to be very considerably reduced for the presence of the screw thread to be detected at all. For the identification of faults in screw thread a further reduction of the limits tolerated is necessary. If however the limits tolerated are overly reduced, even minimum departures in alignment may lead to rejection so that examination of such structures is not possible in practice. The same will apply for example for small holes, filleted intersections or the like. A further disadvantage of the known method is that for the comparison of surface structures and to achieve a good resolution an extremely large memory is required and the comparison operations require a relatively long time. The evaluating equipment needed is accordingly elaborate and expensive.
One object of the present invention is to create a testing method of the type initially mentioned with the aid of which extremely fine structures as well may be reliably identified in a relatively simple fashion and a suitable apparatus for the performance of the method.
This object is to be attained in the invention by deriving a plurality of individual criteria, the overall length, the overall height, the area, the axial alignment, the surface waviness, the position of the center of gravity, from the camera image signal, representing the shape of the respective part, and in that these individual criteria are compared with the individual criteria derived from at leas, master part
The method of the invention offers the advantage that it is now not necessary for all image points of a reject structure to be compared with each other, and it is only the values of the individual criteria derived from the image signal and employed as test criteria which must be compared. There is consequently a reduction in memory requirement and in the complexity needed for comparison as compared with conventional systems. Since these individual criteria identify and test the typical and significant features and structures of the part to be examined, all in all a reliable identification is performed. Significant criteria, which are however small as regards departure in area, as for example screw threads, may be reliably identified thereby, for example by the selection of surface waviness as an individual criterion. By making a skillful selection of the individual criteria it is possible for small elements and fine structures to be individually tested and identified.
The basis of the invention is in this respect that only the marginal parts of areas are relevant for identification and examination, not the full areas themselves lying in between, which accordingly do not have to be tested.
Further advantageous developments of the method of claim 1 are defined in the dependent claims, and an advantageous apparatus for the performance of the method will be defined.
More particularly by different weighting of the individual criteria it becomes possible to reliably identify details which only have a minor effect on the overall shape but which are extremely significant as such.
Owing to the possibility of pre-selecting such individual criteria it is possible to take into account the respective particularities of a part and to optimize identification.
Furthermore for the identification of significant details it is an advantage to divide up the image signal into different portions, each of such portions being evaluated independently of the others as regards the individual criteria. Preferably in this respect the portions are also differently weighted so that even finer and more exact adaptation to the respective particularities of a part becomes possible.
The different weighting of the individual criteria and/or portions is best made adjustable in order to be able to perform optimum adaptation.
For the acquirement of comparison data at least one master part may be subjected to a learn process, the corresponding image signal or the individual criteria derived therefrom being stored in order to be available in the operating mode for comparison.
For rapid adaptation and resetting for different parts to be tested a plurality of different master parts may be subjected to the learning mode, one of such master parts being able to be selected for the comparison. For changing over to another sort of parts to be tested, it is hence only necessary to operate a switch over key, if the other part has already been learned.
By multiple learning of each master part in the learn mode or by learning a plurality of master parts of the same type one after the other an inaccuracy tolerance range may be preset, since all such master parts are to lie in this tolerance range. For example by slight changes in the orientation of the multiply stored or learned master part those changes in orientation may be learned as well, which are to be within the tolerance range.
In the operating mode the sensitivity (tolerance) in identification may be set in at least one stage so that for example a plurality of different quality stages may be preset and sorting of the parts in several sorts is possible, for which the different tolerance conditions can be preset.
Parts to be removed as rejects are best removed from the conveyor means by blowing using at least one compressed air blast. If multi-stage sorting in accordance with different criteria is to take place, the parts on the conveyor means will preferably move past several air blast clearing stations, which remove the parts in accordance with different criteria.
The parts to be removed at one air blast clearing station at least and/or the parts which are not removed are best counted using a counter device in order for example to determine when a desired number of satisfactory parts has been reached.
The counter device may with advantage also be so operated that after reaching a predetermined number of satisfactory parts and/or reject parts the conveyor means and/or a supply means leading to the conveyor means, such as a sorting and straightening up station, is automatically turned off. Furthermore a following machine, as for example a packaging machine, can then be switched off or switched on again, when after a predetermined number of satisfactory parts a package is filled so that the next package can be offered.
As a camera it is best to employ a line camera. This means that there is the advantage that line orientated processing becomes possible, i. e. after each line has been registered corresponding computation and evaluation may take place. Accordingly the evaluation is terminated after the last line has been responded. An evaluation of the overall shape is then unnecessary. Therefore a rapid evaluation is possible with a small memory requirement.
In the case of an advantageous apparatus for the performance of the method in accordance with the invention at least the conveying means and the camera constitute an assembly unit, in which they have a fixed spatial relationship to one another, such assembly unit being arranged in common assembly holder. In this apparatus it is accordingly merely necessary for the common assembly holder to be fixed at a suitable point, no adjustment operations being necessary, because the camera and the conveying means are already set in a fixed spatial relationship on the assembly holder. Immediately after fixation of the assembly unit the apparatus in accordance with the invention is therefore fit for use and a start may be made with the examining operations intended. This apparatus may also in an advantageous fashion be utilized in connection with other examining methods for parts.
The conveying means preferably includes a conveyor belt, the camera preferably being arranged on one side of the conveying means and an illuminating means being arranged on the opposite side thereof in order to obtain images with backlighting, it being possible to cut out other interfering lighting effects.
In order to be able to completely examine the parts at an optimum angle, the camera is best arranged at such an angle to the load surface of the conveyor belt that the bottom limiting line of the image angle range of the camera essentially extends along the load surface.
In order to facilitate operations and for maximum variability of assembly the assembly holder possesses an assembly base provided with a holding rod, on which the conveying means, the camera and more especially the illuminating means are fixed. A removable housing, through which the conveying means extends, contains all components of the apparatus apart from the evaluating means so that on the one hand such accommodated components are protected and on the other hand the result of measurement is not affected by incidence of light from the outside.
A drive motor for the conveying means is best arranged to the side of the conveying means and to the side of the camera in order to ensure a compact arrangement. In order to change the direction of conveying together with the drive motor fixed thereon and the illuminating means the conveying means is so arranged in a re-settable manner that after each rearrangement the top side and the bottom side and furthermore the right hand and the left hand conveying portion are changed over and the drive motor is arranged on the opposite side of the camera so that the same housing may still be employed.
In accordance with an advantageous development the conveying means possesses a more particularly rail-like cover arranged parallel to it, such cover possessing at least one reject removal station, whose air nozzle are directed from the side toward the conveying means for parts which are to be removed. Each removal station in this case comprises preferably several more particularly superposed compressed air nozzles. It is in this manner that the removal stations are integrated in a compact arrangement and protected against contamination by dirt.
The rail-like cover is preferably able to be mounted on both flat sides of the conveying means in order to be able to be replaced on the top side following changing the conveying direction.
In order for example to be able to convey and examine round or rounded parts, the conveying means is so inclined to the side that the conveyed parts are moved along the i rail-like cover.
The control valves for the compressed air fed to the air blast nozzles are protected in the accommodating rail-like cover or in the conveying means against dirt and furthermore do not constitute and danger of injury.
The evaluating device may with advantage connected via a flexible cable bundle with the assembly unit so that this evaluating device also serving as a control device may be arranged or, respectively, mounted at any position.
The evaluating device may with advantage be adapted to serve for control of the conveying means, for receiving and evaluating the camera signals and preferably also for control of the at least one reject removal station. Furthermore the reject removal means preferably possesses counting means for the satisfactory parts and/or the rejected parts.
Moreover the evaluating means can with advantage comprise means for automatic switching off of the conveying means and/or of a supply means of the conveying means on attaining a predetermined number of satisfactory parts and/or rejects. Furthermore it is an advantage for the entire apparatus to be designed as a sorting station for the sorting of differently supplied parts.